Many systems have been devised which deal with control of watering and feeding plants, particularly those of a potted or container-bound variety. One well known type of irrigation system operates on a vacuum pressure release principle wherein water and/or other liquid will not flow by gravity from an air tight receptacle unless air is admitted thereto. Then, when a liquid level drops to the bottom of an air or sensor tube depending from the receptacle, air is permitted to pass up into the receptacle and liquid is discharged from the tube or other means until the level of liquid covers the bottom end of the air or sensor tube thereby shutting off the flow of air and liquid.
Prior plant irrigation systems employing the above described vacuum pressure release principle have generally been inadequate for several reasons. For example, most automatic plant watering systems provide a drop-wise discharge of water and/or other liquid nutrient from above the soil level of the potted plant. Such top watering designs have been found to provide uneven drip-type irrigation to the roots of the potted plant. In addition, watering the potted plant from above has a tendency to push toxic residues in the soil down into the root zone which can cause plant growth problems.
One example of such a system described above is disclosed in U.S. Pat. No. 3,856,205 issued Dec. 24, 1974 to Rohling. Another similar design is shown in U.S. Pat. No. 4,321,937 issued Mar. 30, 1982 to Littlehale. This latter system recognizes that various types of sensors or control elements may be utilized at the bottom of a rigid sensor tube to detect the moisture requirements for a particular plant. However, it is noted that due to the rigidity of the sensor tube, the sensor remains at a particular location within the soil which limits the effectiveness of the irrigation. A further example of a prior art top watering, drip system is set forth in U.S. Pat. No. 4,578,897 issued Apr. 1, 1986 to Pazar et al. This system suffers additionally from disposing the bottom of the plant in a standing pool of water which is conducive to rotting of the roots. Another type of system, in the form of a valve, for regulating irrigation to plants based on soil moisture requirements is described in U.S. Pat. No. 5,113,888 issued May 19, 1992 to Beggs. Instead of using a vacuum, this valve relies upon positive air exit pressure to periodically deliver water to a spray head above the soil so that this device suffers the same top watering control problems as discussed above.
Such predecessor systems have not proved entirely effective and convenient to use, and it remains desirable to provide a plant subirrigation or bottom watering system which selectively transports a free, yet manageable, flow of liquid directly to the plant root zone so as to insure stronger, more vigorous plants. It is also desirable to provide a plant subirrigation system which is more versatile in adjusting the degree of wetness or dryness for a particular plant. It is further desirable to provide a subirrigation system which can be easily installed and simply used with any potted plant, requires no assembly and generally avoids the problems of the prior art systems as set forth previously.